Adding MDD import and export from patch 4969 with modifications, (import and export rvks, MDD is from lightwave AFAIK)

Added Mesh .key .removeAllKeys() and .insertKey() for MDD support (was using NMesh just for keys before)
Since this is aparently an experemental feature in NMesh we may want to change this.

source/blender/python/api2_2x/doc/Mesh.py

@@ -961,6 +961,31 @@ class Mesh:
         and weight is a float value.
     """
 
+  def removeAllKeys():
+    """
+    Remove all mesh keys stored in this mesh.
+    @rtype: bool
+    @return: True if successful or False if the Mesh has no keys.
+    """
+
+  def insertKey(frame = None, type = 'relative'):
+    """
+    Insert a mesh key at the given frame. 
+    @type frame: int
+    @type type: string
+    @param frame: The Scene frame where the mesh key should be inserted.  If
+        None or the arg is not given, the current frame is used.
+    @param type: The mesh key type: 'relative' or 'absolute'.  This is only
+        relevant on meshes with no keys.
+    @warn: This and L{removeAllKeys} were included in this release only to
+        make accessing vertex keys possible, but may not be a proper solution
+        and may be substituted by something better later.  For example, it
+        seems that 'frame' should be kept in the range [1, 100]
+        (the curves can be manually tweaked in the Ipo Curve Editor window in
+        Blender itself later).
+    """
+
+
   def smooth():
     """
     Flattens angle of selected faces. Experimental mesh tool.